Dial-on-Demand Routing (DDR) addresses the need for intermittent network connections over circuit-switched WANs. There are two main methods to configure DDR: legacy DDR and dialer profiles. This document addresses dialer profiles. For information on configuring legacy DDR, please refer to these resources:

The information in this document is based on these software and hardware versions.

Cisco 2503 with Cisco IOS® Software Release Version 12.2(10b)

Cisco 2503 with Cisco IOS Software Release Version 12.2(10b)

Cisco 2520 with Cisco IOS Software Release Version 12.2(10b)

The information presented in this document was created from devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If you work in a live network, ensure that you understand the potential impact of any command before you use it.

Dialer profiles separate logical configurations from the physical interfaces that receive or make calls. Because of this separation, multiple dialer profile configurations can share interfaces such as ISDN, asynchronous modems, or synchronous serial connections. Dialer profiles allow you to bind logical and physical configurations together dynamically on a per call basis. This allows physical interfaces to take on different characteristics based on incoming or outgoing call requirements. Dialer profiles can define encapsulation, access control lists, minimum or maximum calls, and toggle features on or off. Dialer profiles are particularly useful where multiple ISDN B channels are to be used to connect to multiple remote destinations simultaneously. In such a case, one dialer profile can be bound to one set of B channels while another dialer profile can be bound to another set of B channels. This allows the same physical interface to connect to multiple remote destinations simultaneously.

The components of a dialer profile include:

Dialer interfaces - logical entities that use a per-destination dialer profile. You can create any number of dialer interfaces in a router. All configuration settings specific to the destination go in the dialer interface configuration. Each dialer interface uses a dialer pool, which is a pool of physical interfaces (ISDN BRI and PRI, asynchronous-modem, and synchronous serial).

Dialer pool - Each interface references a dialer pool, which is a group of physical interfaces associated with a dialer profile. A physical interface can belong to multiple dialer pools. Contention for a specific physical interface is resolved by configuring the optional priority command.

Physical interfaces - Interfaces in a dialer pool are configured for encapsulation parameters. The interfaces are also configured to identify the dialer pools to which the interface belong. Dialer profiles support PPP and High-Level Data Link Control (HDLC) encapsulation.

dialer idle-timeout seconds - Specifies the idle timer value to use for the call. This timer disconnects the call if no interesting traffic has been transmitted for the specified time. The default is 120 seconds.

dialer fast-idle seconds - Specifies a quick disconnect time if there is another call waiting for the same interface and the interface is idle. The waiting call does not have to wait for the idle timer to expire. The default is 20 seconds.

dialer wait-for-carrier-time seconds - Specifies the time for the carrier time value to use for the call. If no carrier is detected within the specified time, the call is abandoned.

Following is a list of optional map class commands:

map-class dialer class-name - Specifies a map class and enters map class configuration mode. The map-class configuration is linked to a dialer profile with the dialer string # class class-name command applied on the interface dialer mode. The following commands are available in the map class configuration mode:

dialer isdn [speed speed ] [spc] - Specifies the ISDN line speed (64kbps is the default). The spc option is used to specify an ISDN semi-permanent connection.

Following is a list of optional multilink PPP commands:

ppp multilink - Specifies that this dialer interface uses multilink PPP (fragments packets over a bundle of interfaces connected to the same destination). This command is placed on the physical interface for incoming calls and in the dialer interface for outgoing calls.

show dialer [interface type number] - Displays general diagnostic information for interfaces configured for DDR. If the dialer came up properly, the Dialer state is data link layer up message should appear. If physical layer up appears, then the line protocol came up, but the Network Control Protocol (NCP) did not. The Dial reason line shows the source and destination addresses of the packet that initiated the dialing. This show command also displays the timer's configuration and the time before the connection times out.

show isdn status - Ensure that the router is properly communicating with the ISDN switch. In the output, verify that Layer 1 Status is ACTIVE, and that the Layer 2 Status state = MULTIPLE_FRAME_ESTABLISHED appears. This command also displays the number of active calls.

debug isdn q921 - Shows data link layer messages (Layer 2) on the D channel between the router and the ISDN switch. Use this debug if the show isdn status command does not display Layer 1 and Layer 2 up.

This configuration demonstrates how you can dynamically bind logical entities called dialer profiles to physical interfaces on a per call basis. By using dialer profiles, the network is able to connect to remote locations with greater flexibility. Additionally, you can use dialer profiles to better utilize available resources. You can therefore use dialer profiles to overcome many of the shortcomings of legacy DDR.